As may be known, Government and civilian aircraft fleet operators use various fleet management programs to assist in the maintenance and repair of fleet aircraft. Some programs include life history recordings of engine configuration, aircraft subsystem performance, and operating times. All of which is useful in scheduling maintenance intervals and determining mean time before failure (MTBF).
One such management program is associated with monitoring aircraft structural loads, i.e. flight maneuver stresses on the airframe. The prior art implementation of this program includes use of a continuous recording, Flight Loads Recorder (FLR), such as the MXU 553 currently installed on the military F16 A/B aircraft. The purpose is to continuously record sample values of selected flight parameters related to providing a "loads/environment stress survey" for the F16 fleet. In this prior art FLR system the selected flight parameter sampled values are recorded in real time, in a continuous recorder, in a tape, or foil medium. The sampling is performed by a data acquisition unit (DAU) which conditions the sensed signal information for recording in an analog system, and which additionally provides analog-to-digital conversion of the sensed parameter signals for recording in a digital signal system. The sensed data is typically sampled at a 30 HZ sample rate and all samples are stored in fixed frames in the tape recorder unit, requiring extensive signal storage capacity which is feasible only in mechanical systems.
The recorded bulk data is later reduced on the ground by a transcriber/reformatter routine designed to eliminate extraneous data values and to focus on "significant event" data indicative of nonquiescent stress conditions on the aircraft. The ground data reduction process is a combination of multiple pass routines using batch process techniques. The successive pass-throughs of the bulk data provide succeeding quantitative refinements in searching for parameter value extremes, typically using "peak and valley search routines".
The downside with the prior art load recording systems and methods is, in addition to the time required to provide ground data reduction for all of the bulk data continuously recorded during flight, the problems of reliability. Mechanical problems associated with the recorder itself due to the volume of recording, such as: breakage of the tape or foil medium used to record the data, failures of the recorder tape drive, and failure or contamination of the recording heads make data storage unreliable. In many instances the data is not recorded or, if recorded, is less resolute than preferred due to noise or degradation in recording performance. The mechanical recorder failure problems are eliminated by recording the data in solid-state memory, i.e. integrated circuit memory having far higher reliability.
In order for a solid-state memory device to be used for the recording of the real time samples, the data must necessarily be first compressed to reduce data volume prior to storage. This is required due to the comparatively high cost per bit of storage in IC memory. The compression routine would necessarily be a functional equivalent of the prior art routine presently used in the ground data reduction. However, the compression routine would have to operate in situ, i.e. "on the fly" during flight, without benefit of successive pass-throughs as with ground reduction routines. The compression algorithms would, therefore, have to be highly reliable if the compressed data integrity can be ensured to provide accurate "reconstructed" stress profiles.